Air conditioning system with freeze throttling valve

ABSTRACT

An automobile air conditioning system having a liquid accumulator located between the evaporator and the compressor to receive refrigerant from the evaporator. A temperature responsive actuator is connected to a throttling valve in the accumulator to regulate the flow of refrigerant from the evaporator and to maintain refrigerant temperature in the evaporator above a level corresponding to freezing temperatures on the external surfaces of the evaporator. The actuator contains water or a water based solution placed in good heat transfer with refrigerant in the accumulator. When refrigerant falls to a predetermined temperature, the water begins to freeze and the resultant expansion moves the throttling valve toward a more closed position.

United States Patent 1191 Scherer et al.

[ Mar. 26, 1974 AIR CONDITIONING SYSTEM WITH FREEZE TI-IROTTLING VALVE [75] Inventors: Carl A. Scherer, Clarence Center;

Hugh James Muirhead, Sanborn, both of NY.

[73] Assignee: General Motors Corporation,

Detroit, Mich.

[22] Filed: Mar. 26, 1973 211 Appl. No.: 344,748

[52] US. Cl. 62/217, 62/503 [51] Int. Cl. F25b 41/04 [58] Field of Search 62/217, 503, 212, 204, 62/224 [56] References Cited UNITED STATES PATENTS 1,990,663 2/1935 Muttly 62/204 2,187,258 1/1940 Wood 62/217 3.525.234 8/1970 Widdowson 62/217 3,563,053 2/1971 Bottum 62/503 Bottum 62/503 Proctor 62/212 Primary ExaminerMeyer Perlin Attorney, Agent, or Firm-l(. l-l. MacLean, Jr.

57 ABSTRACT An automobile air conditioning system having a liquid accumulator located between the evaporator and the compressor to receive refrigerant from the evaporator.

Atemperature responsive actuator is connected to a throttling valve in the accumulator to regulate the flow of refrigerant from the evaporator and to maintain refrigerant temperature in the evaporator above a level corresponding to freezing temperatures on the external surfaces of the evaporator. The actuator contains water or a water based solution placed in good heat transfer with refrigerant in the accumulator. When refrigerant falls to a predetermined temperature, the water begins to freeze and the resultant expansion moves the throttling valve toward a more closed position.

5 Claims, 5 Drawing Figures PAIENIEDIIARZS I974 33. 798,921

SHEET 2 [IF 2 SILVER IODIDE SOLUTION I:

DISTILLED WATER T I I I I I l I I l 20F 32F TEMPERATURE frr My;

To"I 70 |--EvARoRAToR -I 1 FREEZE-UP 32 I I I I I 28 ,4 I HIGH AMBIENT 24 TEMPERATURE I LOW AMBIENT TEMPERATURE 20 I I4 F I 1 2 MINUTES 4 MINUTES 4 MINUTES I HOUR ACTUATOR SILVER IODIDE ACTUATOR DISTILLED WATER AIR CONDlTlONlNG SYSTEM WlTH FREEZE THROTTLING VALVE This invention relates to automobile air conditioning systems and more particularly to automatic temperature responsive valving to regulate evaporator temperature.

In present automobile air conditioning systems a refrigerant compressor is driven by the automobiles internal combustion engine whose speed varies over a relatively wide range. The pumping or compressing capacity of the compressor is proportional to changes in the engine speed. This variable compressing capacity directly effects the cooling effectiveness of the system since the cooling capacity of the evaporator at any given ambient temperature is limited by heat transfer considerations relating to fin design.

Unfortunately, changes in compressor capacity are not conveniently regulated to make them correspond to the cooling capacity of the evaporator. Thus, in operation under low ambient temperature conditions, the compressor capacity usually exceeds the ability of the evaporator to extract heat from air passing over its exterior surfaces. Under these conditions, refrigerant pressure within the evaporator will decrease due to an excess liquid refrigerant supply and to incomplete vaporization of refrigerant in the evaporator. Also, the increased rate of discharge from the evaporator back to the compressor during high speed operation of the compressor will decrease evaporator pressure and temperature. Refrigerant pressure will eventually decrease below a pressure level which corresponds to a freezing temperature on the exterior fin surfaces of the evaporator. When the fin surface temperature drops below 32 F., frost will usually begin to accumulate thereon. The frost accumulation is undesirable because it decreases the rate of heat transfer between air and the evaporator structure, and eventually will block air flow through the evaporator.

It is desirable to provide means to prevent the refrigerant temperature within the evaporator from falling below a level corresponding to freezing temperatures on the exterior fin surfaces of the evaporator. The present air conditioning system includes a temperature responsive throttling valve located in a refrigerant accumulator which is located between the evaporator and the compressor. Under the aforedescribed conditions of low ambient temperatures and excess compressor capacity, the valve moves toward a closed position to restrict the flow of refrigerant from the evaporator to the compressor. The restriction or throttling of refrigerant flow maintains sufficient refrigerant in the evaporator to thereby increase evaporator pressure and its corresponding temperature.

Previously, throttling valves have been utilized which sense evaporator pressure to control the pressure in the evaporator, for example by an evacuated bellows. Earlier systems have also used external sensors or feelers on the evaporator's exterior to sense frost buildup and to activate defrost means such as a compressor cutoff.

The present evaporator temperature regulator consists ofa throttling valve assembly within an accumulator which is located between the evaporator and the compressor. The valve regulates the flow of refrigerant from the evaporator to the compressor by movement of a thermally responsive actuator located upstream from the valve member which is located adjacent the accumulator outlet. The actuator responds to freezing level temperatures of refrigerant by moving the valve member toward a closed position. This maintains the evaporator temperature above the level to prevent frost accumulation on the evaporators external surfaces.

The illustrated embodiment of the valve actuator includes an elongated tubular member which is filled with water having a freeze point of about 32 F. An integrally connected portion of the actuator has corrugated side walls which form a hollow, bellows-like enclosure, the interior of which is fluidly connected to the interior of the tubular portion. The bellows portion contains a fluid such as oil which is immiscible with respect to the aqueous solution in the tubular portion. The oil has solidification temperature substantially below 32 F. When the water within the tubular portion freezes, it expands to pressurize the adjacent oilfilled bellows portion. This will cause the bellows to be axially extended. A valve member is connected to the bellows and is moved toward a closed position with respect to a valve seat to restrict refrigerant flow from the accumulator and the evaporator.

The throttling valve described above is enclosed within the liquid accumulator assembly. The accumulator stores excess refrigerant which will make up for small leakages of refrigerant. The arrangement of the inlet and outlet causes separation of vapor and liquid so that mostly vaporous refrigerant passes to the compressor. The accumulator inlet is attached to the evaporator and the outlet is connected to the compressor inlet. The aforementioned throttling valve assembly is supported within the accumulator with the tubular portion located upstream from a valve member adjacent the outlet. This permits the throttling valve to always respond to refrigerant temperatures in the evaporator (as transmitted to the accumulator). A location of the actuator downstream from the valve would incorrectly sense evaporator temperature since once the valve begins to close, refrigerant flow will be decreased and the refrigerant temperature may be effected by any throttling action during passage past the valve.

The bellows portion of the actuator may be attached above the tubular portion or below it, depending on whether the immiscible liquid used in the bellows is lighter or heavier than the aqueous solution. The reason a nonfreezing substance is enclosed in a bellows portion is to prevent damage to the corrugated, thin walled sides of bellows which might be caused by the repeated solidification and expansion of water therein.

The air conditioning compressor is lubricated by a quantity of oil which is carried by the refrigerant charge. To maintain a continuous passage of oil through the air conditioning system and to t he compressor for lubrication, a bypass means is provided around the throttling valve. An oil pickup tube extends toward the bottom of the accumulator and in bypass to the valve. Oil is drawn upward through the oil pickup tube to a location downstream from the valve and then to the compressor. When the throttling valve is closed, the pressure in the suction line is relatively low compared to the pressure within the accumulator and this draws the oil through the oil pickup tube into the suction line.

A desirable control temperature for an evaporator is dependent on its structure. General Motors automobiles employ a parallel pass type evaporator characterized by a minimal pressure drop from its inlet to its outlet. Consequently, a water filled actuator (32 F control) works well. With a series type tube and fin evaporator having a greater pressure drop, a water-alcohol or glycol filled actuator with a lower control point (perhaps 26F) may work well since the average temperature b etiveen the inlet to outlet will be sufficient to prevent frost formation. Also, water-salt solutions may be used in place of alcohol or glycol.

It has been found that distilled water may be subjected to temperatures as low as 21 F. before the first ice crystal will form. The actual temperature at which ice forms may be labeled the crystallization tempera ture. Its value will be dependent on the method of testing as it is affected by the degree of fluid agitation, the rate of temperature change and flow rates. With a crystallization temperature as low as 21 F, water will make an undesirable control fluid. With water in the actuator, the evaporator may decrease to around 21 F. Before anyice forms in the actuator, the frost may accumulate to a sufficient degree to block air flow through the evaporator.

It has been found that a mixture or suspension of water and a small quantity of silver iodide provides satisfactory control fluid for the actuator. Utilizing the same test method which was used to measure a crystallization temperature of 21 F for distilled water, a crystallization temperature of about 27.5 F was recorded for the mixture of water and silver iodide. The insolubility of silver iodide insures that salt crystals will be present in the actuator on which ice crystals may grow.

The characteristic of a crystallization temperature below the freezing temperature is significant only upon first energizing or activating the air conditioning system. When the system is first activated, the temperature of refrigerant in the evaporator is rapidly lowered from ambient levels to a sub-freezing level. Subfreezing temperatures of refrigerant in the evaporator are desirable for a short time under low ambient temperature conditions and for a longer time under higher ambient temperature conditions. The sub-freezing temperatures provide a rapid cool down of the initially warm air in the passenger compartment. However, if these low temperatures persist for too long a period, the airwill cool and frost will begin to block the evaporator. Using distilled water in the actuator with a 21 F crystallization temperature, the first ice crystals may not form in time to prevent blockage of the evaporator. The 27.5 F crystallization temperature of the silver iodide-water mixture, however, is high enough to form ice crystals in the actuator after an initial cool down" of the passenger compartment. Immediately after the first ice crystal is formed, the temperature of water increases to 32 F. Thereafter, the actuator controls the throttling valve to maintain a 32 F temperature of refrigerant in the accumulator and evaporator.

Therefore, an object of the present invention is to provide a simple and accurate evaporator temperature controller housed within a liquid accumulator to continually sense and control refrigerant temperature therein.

A further object of the present invention is to provide an evaporator temperature controller utilizing a freeze actuator which contains a thermally expandable water based fluid in heat transfer relation to refrigerant contain'ed in a liquid accumulator fluidly connected to the evaporator for continuously sensing refrigerant temperature of the evaporator and operating a throttling valve located at the outlet of the accumulator in accordance with freeze characteristics of the fluid.

A still further object of the present invention is to provide a simple and highly accurate evaporator temperature controller including a throttling valve located downstream from a valve actuator which contains a mixture of water and silver iodide and is placed in good heat transfer relation to refrigerant from the evaporator to initially cause icein said actuator to form at a temperature closer to the freeze characteristics of the water or water based solution than otherwise would occur.

A still further object of the present invention is to provide a simple and durable temperature controller including a freeze actuator with a container portion having rigid walls enclosing a freezable fluid and with an interconnected portion having relatively flexible walls and containing a liquid material which remains in a liquid state substantially below the freeze temperature of the fluid in the container portion.

Further objects and advantages of the present invention will be readily apparent from the following detailed description, reference being bad to the accompanying drawings in which a preferred embodiment is clearly shown.

IN THE DRAWINGS FIG. 1 is a schematic illustration of an automobile air conditioning system;

FIG. 2 is a vertical sectioned view of the liquid accumulator shown in FIG. 1 enclosing the subject freeze actuated throttling valve assembly;

FIG. 3 is a bar graph illustrating the freeze characteristics of two fluids with the crystallization temperature at the left end of the bar and the freeze temperature at the right end of the bar;

FIG. 4 is a plot of refrigerant temperature versus time in the evaporator-accumulator under low and high amy bient conditions and utilizing a silver iodide-water mixture in the valve actuator; and

FIG. 5 is a plot of refrigerant temperature versus time in the evaporator-accumulator utilizing distilled water in the valve actuator and showing resultant core freezeup of the evaporator.

In FIG. 1 of the drawings, an air conditioning system is illustrated including a refrigerant compressor 10. The drive shaft of the compressor 10 is connected to a pulley assembly 12 which is driven by an engine of the automobile by belts (not shown) extending through grooves 14 of the pulley 12. The outlet 16 of compressor 10 is attached by fitting 18 to a flexible hose 2 0 which is connected to the inlet 22 of condenser. 24 by fitting 26. The condenser 24 is adapted to be located near the front of the automobile to be exposed to a flow of air into the grille for cooling and liquefying the warm refrigerant therein. The outlet 28 of the condenser is sluidly connected to a capillary type expander 30 to reduce the pressure of liquid refrigerant received from condenser 24. For more details of the structure of the capillary expander shown in FIG. 1, reference is made to a copending United States Patent Application Serial No. 302,108, filed Oct. 30, 1972, and assigned to General Motors Corporation.

The expander 30 is connected to the inlet 32 of an evaporator 34 in which liquid refrigerant is vaporized in parallel tubes 36, each having connected fluid conveying portions and exterior finned surfaces formed integrally therewith. The evaporator 34 has an outlet 38 which is connected to an inlet of a liquid accumulator 40. The liquid accumulator 40 separates liquid from vaporous refrigerant and discharges vaporous refrigerant through an outlet into a suction line 42. Line 42 is connected by fitting 44 to the inlet 46 of compressor 10.

As previously stated, when the air conditioning system is operated under low ambient temperature conditions there is frequently insufficient heat transfer from the cool air flowing over the tubes 36 of evaporator 34. Consequently, the heat transferred is insufficient to vaporize refrigerant quickly enough within the evaporator to maintain its internal pressure above a level corresponding to a refrigerant temperature about 32 F. The present invention provides a thermally responsive throttling valve assembly 48 within the accumulator 40 to restrict the flow of refrigerant from the evaporator under these low ambient temperature conditions and consequently increase the internal pressure of the evaporator.

The accumulator consists of a tubular member 50 having a closed end 52 and an interior space 54. An open upper end of the tubular member 50 is covered by an end member 56 which has an inlet portion 58 adapted to be fluidly connected to the evaporator outlet 38. An outlet portion 60 is adapted to be fluidly connected to the suction line 42. An inlet passage 62 introduces a mixture of liquid and vaporous refrigerant into interior 54 from evaporator 34. A weld 64'between end member 56 and tubular member-50 seals the refrigerant in space 54 and an O-ring 66 supported within a groove 68 prevents leakage between members 50, 56. Refrigernat is discharged from space 54 through .an outlet passage 70 in the end member 56. It then passes through suction line 42 to the inlet 46 of compressor 10.

A desiccant assembly 72 is supported in the bottom of the interior space 54 by a support member 74. The desiccant 72 includes an outer skin 76 of porous material which encloses a quantity of silicagel 78. The silica gel absorbs any moisture which happensto be mixed with refrigerant.

Refrigerant temperatures in the evaporator are directly controlled by throttling valve assembly 48 supported in space 54 by a tubular valve seat member 80. An upper end of member 80resides in a groove82 formed within the end member 56. The valve seat member 80 supports an O-ring '84 withingroove 86 to prevent refrigerant leakage in bypass to'the valve. An expansible snap ring retainer-88 holds the valve seat member within recess-82. The valve seat'member-80 includes a partition wall90 whichrhas a passage'92 therein and a valve seat portion 94 formed on the upper end of the wall 90. Normally, refrigerant flows through the inlet passage 62 into the interior 54 of the accumulator where liquid refrigerant isseparated and directed toward the bottom of the accumulator until vaporized while vaporous refrigerant passes through the passage 92 to the outlet 70 of the accumulator and thence through suction line 42 tothe inlet-46 of compressor 10.

The valve seat member includes a tubular support portion-96 upstream from the passage 92 which encircles a temperature responsive valve actuator 98 to permit it to reciprocate in thepassage 92. The actuator 98 includes an elongated tubular portion 100 extending towards the lower end 52 of the accumulator 40. An annular valve member 102 is attached around the upper end of the tubular member 100 adjacent the valve seat 94. A hollow bellows portion 106 is attached to the valve member 102 downstream from valve seat 94. It comprises a generally cylindrical member formed by a corrugated side wall 108. The interior of the tubular portion 100 and the bellows portion 108 are fluidly interconnected by a'bore 104 .through a valve member 102. The tubular portion 100 is nearly filled with fluid 111 which has a desired freezing temperature control of 32 F for the illustrated parallel pass evaporator. The remainder of the tubular portion 100 and the interior of the bellows portion 106 is filled with a liquid 113 such as oil which has a solidification temperature substantially below 32 F and is immiscible with respect to the water.

When refrigerant in the interior of accumulator 40 decreases in temperature below 32 F the water 111 will crystallize and begin to solidify. When this happens, its volume is increased and the meniscus 115 formed between the solution 111 and the liquid 113 will be moved upward in FIG. 2 and exert a pressure upon the flexible walls 108 of the bellows 106. This causes the bellows 106 to expand axially. The upper end of the bellows portion 106 is attached by a base portion 117 to an override retainer 119 which is held against the valve seat member 80 by an override spring 121. When the bellows 106 is expanded axially, the valve member 102 and the tubular member 100 move downward in FIG. 2 against the resisting force of valve spring 123 toward valve seat 94. This restricts therefri gerant flow through passage 92. When all of the fluid 111 is solidified, the valve member 102 should engage valve seat 94 to completely block refrigerant flow through passage 92. If further expansion of the fluid 1.1.1 in the tubular member 98 occurs after valve member =102 engages valve seat 94 the bellows 106 will move retainer 119 upward in H6. 2 against override spring 121. This relieves excess pressure of the valve member102 on valve seat 94 which otherwisemight damage the freeze actuator 98. The use of override retainer 1'19 and spring 121 has another importantfunction or advantage other than the protection of the actu- .ator structure. The override provision provides sufficient flexibility so that the valve assembly does not require special calibration. The valve will automatically ,position itself so as to control at 32 F when thefluid is water.

Aspreviously stated, the compressor1l0 is lubricated by oil which is carried along with the refrigerant through the system. A natural place for oil to collect in ber80 to draw oil from thebottom of the accumulator 40 and discharge it downstream from valve member 102. A small orifice 127 is provided in the valve seat member 80 to meter sufficient oil to the compressor. When the valve 102 is in a closed position blocking passage 92, the pressure downstream from the valve 102 is substantially less than in the interior 54 of the accumulator 40, and thus the pressure difference between the interior 54 and the outlet 70 of the accumulator is the motive force for lifting oil through the pickup tube 125.

An important feature of the present invention is the provision of an oil-filled bellows portion fluidly connected to the water-filled tubular portion of the freeze actuator. When the fluid within the tubular portion begins to solidify and expand, great forces are developed in the actuator which might damage the relatively thin walled bellows portion if the freezable fluid engaged the bellows. Any immiscible liquid such as oil can be used in the bellows portion as long as its solidification temperature is substantially below that of the working fluid in portion 100. When oil is used, the bellows portion 106 is located above the tubular portion 100 since oil is lighter than water and thus will collect in the top of the freeze actuator. However, if another immiscible liquid is used which is heavier than water, it is contemplated that the bellows portion 106 could be located below the tubular portion 100 to achieve similar results.

Because of a temperature gradient between the fluid conveying portions of tubes 36 of evaporator 34 and the exterior or finned portions of the evaporator, the temperature of refrigerant within the evaporator may decrease slightly below 32 F without causing the evaporators exterior surfaces from falling below 32 F. The level to which the refrigerant temperature may decrease below 32, of course, is dependent upon the structure of the evaporator itself and the ambient temperature. I

According to the previous paragraph, an ideal fluid for use in the freeze actuator 921 would be a liquid which changes to a solid state at 32F. Pure water theoretically should undergo a change of state from liquid to solid at 32 F and expand in the process. However, tests conducted with distilled water have disclosed that it can be subjected to a substantially lower temperature before any crystallization of solidification begins. This is shown in FIG. 3. It can be observed from the graph that the freezing point of the particular sample of distilled water tested was about 32 F. However, the water in a still environment was subjected to temperatures as low as 20.5 F before ice crystals formed. After the first crystal formed, the mass of water and ice almost instantaneously increased in temperature to about 32 F. The temperature at which ice formation beings is termed the crystallization temperature and is indicated by the left end of the bar in FIG. 3. It is apparent that distilled water alone is not an ideal fluid for use in the actuator 98. If the refrigerant temperature in the evaporator is allowed to drop to almost 20 F before the throttling valve 102 is moved toward a closed position, much frost would form upon the exterior surface of the evaporator. Most likely, frost formation would soon block air flow through the evaporator core and thus greatly decrease the heat transfer to the refrigerant. This would further compound the icing problem. FIG. illustrates what is likely to occur if water alone were used in an actuator of this type. Note the extended period of time which elapses before a frozen core thaws out even after the actuator freezes and closes the throttling valve. This is due to the decreased heat transfer explained above.

It has been discovered that a mixture or suspension of silver iodide in water has a freezing temperature of about 32 F and a crystallization temperature somewhere around 28 F. Thus, as the refrigerant temperature in the evaporator falls below 28 F, crystallization in the solution begins and the freeze actuator begins to control at about 32 F by moving the throttling valve toward a more closed position and thus increasing the temperature of the refrigerant within the evaporator. It is apparent that a mixture of water and silver iodide is a desirable fluid for filling the tubular portion I00 of freeze actuator 98. The freeze characteristics of the silver iodide mixture used in the present embodiment is illustrated in FIG. 3. The left end of the bar indicates its crystallization temperature and the right end indicates the freezing temperature. The 275 F crystallization temperature is high enough to prevent frost accumulation on the exterior surface of the evaporator.

FIG. 4 illustrates the functional operation of the subject freeze actuated throttling valve under both high and low ambient temperature operation. When the'air conditioning system is activated under low ambient conditions, the refrigerant temperature quickly falls to a value below the crystallization temperature. Then ice begins to form and the actuator begins controlling at 32 F by moving the throttling valve toward a closed position. Consequently, the refrigerant temperature increases and moves toward 32 F. Because of the rather limited heat transfer, the refrigerant temperature overshoots 32 F and the freeze actuator responds by further opening the throttling valve which reduces refrig' erant temperature. After a few cycles the actuator maintains refrigerant temperature at about 32 F.

When the air conditioning system is activated under high ambient temperature conditions, the refrigerant temperature quickly decreases toward the crystallization temperature. Because of the increased heat transfer necessary to cool the warm air, a longer period of time is consumed before crystallization is initiated. The increased heat transfer also slows the response of the evaporator refrigerant to changes in temperature and thus there is less overshoot than under low ambient operation. Once crystallization is initiated the actuator begins controlling at 32 F. and the throttling valve is moved toward a closed position which increases refrigerant temperature. When refrigerant temperature increases to about 32 F., the actuator moves the valve toward a more open position and adjusts to maintain the 32 F. temperature.

While the embodiment illustrated is a preferred embodiment, other embodiments may be adapted without falling outside the scope of the following claims.

What is claimed is as follows:

1. An automobile air conditioning system eompris ing: a refrigerant compressor having an inlet and an outlet; a condenser fluidly connected to the outlet of said compressor for liquefying and cooling refrigerant received therefrom; expansion means fluidly connected to said condenser for receiving refrigerant therefrom and for decreasing refrigerant pressure; an evaporator fluidly connected to said expansion means for receiving refrigerant therefrom and for vaporizing refrigerant by the absorption of heat from air passing over the exterior surfaces of the evaporator; a liquid accumulator between said evaporator and said compressor for separating vaporous refrigerant from liquid refrigerant and passing mostly vaporousrefrigerant to said compressor; said accumulator including a lower portion to contain liquid refrigerant and an upper portion having an inlet for conducting refrigerant into the interior of said accummulator and an outlet for discharging refrigerant therefrom; a valve seat member supported within the interior of said accumulator between said inlet and said outlet and having a passage therethrough for conducting refrigerant from the accumulator interior to said outlet; said valve seat member supporting an elongated thermally responsive valve actuator; said valve actuator including an elongated tubular portion connected to an axially extendable bellows portion; said tubular portion being located in the interior of said accumulator which is directly connected to the evaporator by said inlet; an aqueous solution in said tubular portion which freezes at a temperature of about 32F. and upon solidification expands to pressurize and bellows portion and cause it to axially extend; a throttling valve member operably connected to said valve actuator and located downstream from said tubular portion of said valve actuator and movable thereby with respect to said valve seat member and said passage therein to regulate the passage of refrigerant between the interior of said accumulator and said outlet in response to changes in the refrigerant temperature within said accumulator whereby the temperature of refrigerant within the evaporator is maintained at about 32F. which is high enough to prevent accumulation of frost on said evaporators exterior surfaces.

2. An automobile air conditioning system comprising: a refrigerant compressor having an inlet and an outlet; a condenser fluidly connected to the outlet of said compressor for liquefying and cooling refrigerant received therefrom; expansion means fluidly connected to said condenser for receiving refrigerant therefrom and for decreasing refrigerant pressure; an evaporator fluidly connected to said expansion means for receiving refrigerant therefrom and for vaporizing refrigerant by the absorption of heat from air passing over the exterior surfaces of the evaporator; a liquid accumulator between said evaporator and said compressor for separating vaporous refrigerant from liquid refrigerant and passing mostly vaporous refrigerant to said compressor; said accumulator including a lower portion to contain liquid refrigerant and an upper portion having an inlet for conducting refrigerant into the interior of said accumulator and an outlet for discharging refrigerant therefrom; a valve seat member supported within the interior of said accumulator between said inlet and said outlet and having a passage therethrough for conducting refrigerant from the accumulator interior to said outlet; said valve seat member supporting an elongated thermally responsive valve actuator; said valve actuator including an elongated tubular portion connected to an axially extendable bellows portion; said tubular portion being located in the interior of said accumulator which is directly connected to the evaporator by said inlet; an aqueous solution in said tubular portion which freezes at a temperature of about 32 F. and upon solification expands to pressurize said bellows portion and cause it to axially extend; a throttling valve member operably connected to said valve actuator and located downstream from said tubular portion of said valve actuator and movable thereby with respect to said valve seat member and said passage therein to regulate the passage of refrigerant between the interior of said accumulator and said outletin response to changes in the refrigerant temperature within said accumulator whereby the temperature of refrigerant within the evaporator is maintained at about 32 F. which is high enough to prevent the accumulation of frost on said evaporators exterior surfaces; an oil pickup tube within said accumulator interior and extending from the bottom of said accumulator through said valve seat member to a point downstream from said throttling valve for conducting oil which collects in said accumulator to said compressor wherever said valve member is inv a closed position; a small diameter orifice in fluid connection with saidoil pickup tube for controlling the flow of oil through said oil pickup tube.

3. An automobile air conditioning system comprising: a refrigerant compressor having an inlet and an outlet; a condenser fluidly connected to the outlet of said compressor for liquefying and cooling refrigerant received therefrom; expansion means fluidly connected to said condenser for receiving refrigerant therefrom and for decreasing refrigerant pressure; an evaporator fluidly connected to said expansion means for receiving refrigerant therefrom and for vaporizing refrigerant by the absorption of heat from air passing over the exterior surfaces of the evaporator; a liquid accumulator between said evaporator and said compressor for separating vaporous refrigerant from liquid refrigerant and passing mostly vaporous refrigerant to said compressor; said accumulator including a lower portion to contain liquid refrigerant and an upper portion having an inlet for conducting refrigerant into the interior of said accumulator and an outlet for discharging refrigerant therefrom to the compressor; a valve seat member supported within the interior of said accumulator between said inlet and said outlet and having a passage therethrough for conducting refrigerant from the accumulator interior to said outlet; said valve seat member supporting an elongated thermally responsive valve actuator; said valve actuator including an elongated tubular portion connected to an axially extendable bellows portion; said tubular portion being located in the interior of said accumulator which is directly connected to the evaporator by said inlet; an aqueous solution filling said tubular portion and having a freezing temperature of about 32F.; an immiscible liquid with respect to the water filling the interior of said bellows portion and having a solidification temperature substantially below 32F.; a throttling valve member operably connected to said valve actuator and located downstream from said tubular portion of said valve actuator to continuously expose said tubular portion to refrigerant in said accumulator independently of the position of said throttling valve; said throttling valve being movable with said actuator and with respect to said passage in said valve seat member whereby the growth of ice crystals in said aqueous solution contained in said tubular portion when refrigerant temperature decreases below 32F. causes pressurization of the immiscible liquid in said bellows portion and axially expands said bellows portion to move said throttling valve toward a more closed position with respect to said valve seat passage to restrict refrigerant flow from said evaporator and thus control the temperature of refrigerant in said evaporator at a value of about 32F. by the alternating closing and opening of said valve seat passage in proportion to the quantity of ice crystals formed in the solution.

4. An automobile air conditioning system comprising: a refrigerant compressor having an inlet and an outlet; a condenser fluidly connected to the outlet of said compressor for liquefying and cooling refrigerant received therefrom; expansion means fluidly connected to said condenser for receiving refrigerant therefrom and for decreasing refrigerant pressure; an evaporator fluidly connected to said expansion means for receiving refrigerant therefrom and for vaporizing refrigerant by the absorption of heat from air passing over the exterior surfaces of said evaporator; a liquid accumulator between said evaporator and said compressor for separating vaporous refrigerant from liquid refrigerant and passing mostly vaporous refrigerant to said compressor; said accumulator including a lower portion to contain liquid refrigerant and an upper portion having an inlet for conducting refrigerant from said evaporator into the interior of said accumulator and an outlet for discharging refrigerant' from said accumulator to said compressor; a valve seat member supported within the interior of said accumulator between said inlet and said outlet and having a passage therethrough connecting the interior of the accumulator with said outlet; an elongated thermally responsive valve actuator supported by said valve seat member; said valve actuator including an elongated tubular portion connected to an axially extendable bellows portion; said bellows portion having a sidewall with a corrugated configuration to enable the bellows to be extended in an axial direction and to move said throttling valve with respect to said valve seat member; said tubular portion being located in the interior of said accumulator which is directly connected to the evaporator by said inlet; an aqueous solution filling said tubular portion and having a freezing temperature of about 32F; an immiscible liquid with respect to water filling the interior of said bellows portion and having a solidification temperature substantially below 32F; a throttling valve member operably connected to said valve actuator and located downstream from said tubular portion to continuously expose said tubular portion to refrigerant in said accumulator independently of the position of said throttling valve; said throttling valve being moved by said actuator and with respect to said passage in said valve seat member; said aqueous solution consisting of a saturated solution of water and silver iodide having a crystallization temperature greater than for pure water whereby ice crystals in said silver iodide solution first begin to form at a temperature of about 27F. which subsequently pressurizes the immiscible liquid in said bellows to cause said bellows to axially extend and move said throttling valve toward said valve seat memher to restrict refrigerant flow through said passage and thus control the temperature of refrigerant in said evaporator at a value of about 32F. by the alternating closing and opening of said valve seat passage in proportion to the quantity of ice crystals formed in the solution.

5. Evaporator temperature control means for an automobile air conditioning system including in series flow relation; a compressor, a condenser; expansion means for reducing refrigerant pressure and an evaporator: a combination refrigerant accumulator and thermally responsive evaporator temperature control assembly placed between the evaporator and the compressor inlet; said accumulator including a lower portion for holding liquid refrigerant and an upper portion having an inlet for conducting refrigerant into the interior of the accumulator and an outlet for discharging refrigerant therefrom; a valve seat member supported within the interior of said accumulator between said inlet and said outlet and having a passage therethrough for conducting refrigerant from the interior of the accumulator to said outlet; said valve seat member encircling an elongated thermally responsive valve actuator; said valve actuator including an elongated tubular portion connected to an axially extendable bellows portion; said tubular portion being located in the interior of said accumulator which is directly connected to the evaporator by said inlet; an aqueous solution in said tubular portion which freezes at a temperature of about 32 F; an immiscible liquid with respect to water filling the bellows interior and having a solidification temperature substantially below 32 F; a throttling valve member operably connected to said valve actuator and located downstream from said tubular portion to continuously expose said tubular portion and the aqueous solution therein to refrigerant in said accumulator independently of the position of said throttling valve; said aqueous solution consisting of a saturated solution of water and silver iodide having a crystallization temper ature greater than for pure water whereby ice crystals in said aqueous solution first begin to form at a temperature of about 27 F which resultantly produces expan sion within the tubular portion to pressurize the immiscible liquid within said bellows portion to cause said bellows to extend axially and move said throttling valve toward said valve seat member to restrict refrigerant flow through said passage and thus control the refrigerant temperature within the evaporator at a value of about 32 F by the alternating closing and opening of said valve seat passage in proportion to the quantity of ice crystals formed in the solution. 

1. An automobile air conditioning system comprising: a refrigerant compressor having an inlet and an outlet; a condenser fluidly connected to the outlet of said compressor for liquefying and cooling refrigerant received therefrom; expansion means fluidly connected to said condenser for receiving refrigerant therefrom and for decreasing refrigerant pressure; an evaporator fluidly connected to said expansion means for receiving refrigerant therefrom and for vaporizing refrigerant by the absorption of heat from air passing over the exterior surfaces of the evaporator; a liquid accumulator between said evaporator and said compressor for separating vaporous refrigerant from liquid refrigerant and passing mostly vaporous refrigerant to said compressor; said accumulator including a lower portion to contain liquid refrigerant and an upper portion having an inlet for conducting refrigerant into the interior of said accummulator and an outlet for discharging refrigerant therefrom; a valve seat member supported within the interior of said accumulator between said inlet and said outlet and having a passage therethrough for conducting refrigerant from the accumulator interior to said outlet; said valve seat member supporting an elongated thermally responsive valve actuator; said valve actuator including an elongated tubular portion connected to an axially extendable bellows portion; said tubular portion being located in the interior of said accumulator which is directly connected to the evaporator by said inlet; an aqueous solution in said tubular portion which freezes at a temperature of about 32*F. and upon solidification expands to pressurize and bellows portion and cause it to axially extend; a throttling valve member operably connected to said valve actuator and located downstream from said tubular portion of said valve actuator and movable thereby with respect to said valve seat member and said passage therein to regulate the passage of refrigerant between the interior of said accumulator and said outlet in response to changes in the refrigerant temperature within said accumulator whereby the temperature of refrigerant within the evaporator is maintained at about 32*F. which is high enough to prevent accumulation of frost on said evaporator''s exterior surfaces.
 2. An automobile air conditioning system comprising: a refrigerant compressor having an inlet and an outlet; a condenser fluidly connected to the outlet of said compressor for liquefying and cooling refrigerant received therefrom; expansion means fluidly connected to said condenser for receiving refrigerant therefrom and for decreasing refrigerant pressure; an evaporator fluidly connected to said expansion means for receiving refrigerant therefrom and for vaporizing refrigerant by the absorption of heat from air passing over the exterior surfaces of the evaporator; a liquid accumulator between said evaporator and said compressor for separating vaporous refrigerant from liquid refrigerant and passing mostly vaporous refrigerant to said compressor; said accumulator including a lower portion to contain liquid refrigerant and an upper portion having an inlet for conducting refrigerant into the interior of said accumulator and an outlet for discharging refrigerant therefrom; a valve seat member supported within the Interior of said accumulator between said inlet and said outlet and having a passage therethrough for conducting refrigerant from the accumulator interior to said outlet; said valve seat member supporting an elongated thermally responsive valve actuator; said valve actuator including an elongated tubular portion connected to an axially extendable bellows portion; said tubular portion being located in the interior of said accumulator which is directly connected to the evaporator by said inlet; an aqueous solution in said tubular portion which freezes at a temperature of about 32* F. and upon solification expands to pressurize said bellows portion and cause it to axially extend; a throttling valve member operably connected to said valve actuator and located downstream from said tubular portion of said valve actuator and movable thereby with respect to said valve seat member and said passage therein to regulate the passage of refrigerant between the interior of said accumulator and said outlet in response to changes in the refrigerant temperature within said accumulator whereby the temperature of refrigerant within the evaporator is maintained at about 32* F. which is high enough to prevent the accumulation of frost on said evaporator''s exterior surfaces; an oil pickup tube within said accumulator interior and extending from the bottom of said accumulator through said valve seat member to a point downstream from said throttling valve for conducting oil which collects in said accumulator to said compressor wherever said valve member is in a closed position; a small diameter orifice in fluid connection with said oil pickup tube for controlling the flow of oil through said oil pickup tube.
 3. An automobile air conditioning system comprising: a refrigerant compressor having an inlet and an outlet; a condenser fluidly connected to the outlet of said compressor for liquefying and cooling refrigerant received therefrom; expansion means fluidly connected to said condenser for receiving refrigerant therefrom and for decreasing refrigerant pressure; an evaporator fluidly connected to said expansion means for receiving refrigerant therefrom and for vaporizing refrigerant by the absorption of heat from air passing over the exterior surfaces of the evaporator; a liquid accumulator between said evaporator and said compressor for separating vaporous refrigerant from liquid refrigerant and passing mostly vaporous refrigerant to said compressor; said accumulator including a lower portion to contain liquid refrigerant and an upper portion having an inlet for conducting refrigerant into the interior of said accumulator and an outlet for discharging refrigerant therefrom to the compressor; a valve seat member supported within the interior of said accumulator between said inlet and said outlet and having a passage therethrough for conducting refrigerant from the accumulator interior to said outlet; said valve seat member supporting an elongated thermally responsive valve actuator; said valve actuator including an elongated tubular portion connected to an axially extendable bellows portion; said tubular portion being located in the interior of said accumulator which is directly connected to the evaporator by said inlet; an aqueous solution filling said tubular portion and having a freezing temperature of about 32*F.; an immiscible liquid with respect to the water filling the interior of said bellows portion and having a solidification temperature substantially below 32*F.; a throttling valve member operably connected to said valve actuator and located downstream from said tubular portion of said valve actuator to continuously expose said tubular portion to refrigerant in said accumulator independently of the position of said throttling valve; said throttling valve being movable with said actuator and with respect to said passage in said valve seat member whereby the growth of ice crystals in said aqueous solution contained in said tubular portion when reFrigerant temperature decreases below 32*F. causes pressurization of the immiscible liquid in said bellows portion and axially expands said bellows portion to move said throttling valve toward a more closed position with respect to said valve seat passage to restrict refrigerant flow from said evaporator and thus control the temperature of refrigerant in said evaporator at a value of about 32*F. by the alternating closing and opening of said valve seat passage in proportion to the quantity of ice crystals formed in the solution.
 4. An automobile air conditioning system comprising: a refrigerant compressor having an inlet and an outlet; a condenser fluidly connected to the outlet of said compressor for liquefying and cooling refrigerant received therefrom; expansion means fluidly connected to said condenser for receiving refrigerant therefrom and for decreasing refrigerant pressure; an evaporator fluidly connected to said expansion means for receiving refrigerant therefrom and for vaporizing refrigerant by the absorption of heat from air passing over the exterior surfaces of said evaporator; a liquid accumulator between said evaporator and said compressor for separating vaporous refrigerant from liquid refrigerant and passing mostly vaporous refrigerant to said compressor; said accumulator including a lower portion to contain liquid refrigerant and an upper portion having an inlet for conducting refrigerant from said evaporator into the interior of said accumulator and an outlet for discharging refrigerant from said accumulator to said compressor; a valve seat member supported within the interior of said accumulator between said inlet and said outlet and having a passage therethrough connecting the interior of the accumulator with said outlet; an elongated thermally responsive valve actuator supported by said valve seat member; said valve actuator including an elongated tubular portion connected to an axially extendable bellows portion; said bellows portion having a sidewall with a corrugated configuration to enable the bellows to be extended in an axial direction and to move said throttling valve with respect to said valve seat member; said tubular portion being located in the interior of said accumulator which is directly connected to the evaporator by said inlet; an aqueous solution filling said tubular portion and having a freezing temperature of about 32*F.; an immiscible liquid with respect to water filling the interior of said bellows portion and having a solidification temperature substantially below 32*F; a throttling valve member operably connected to said valve actuator and located downstream from said tubular portion to continuously expose said tubular portion to refrigerant in said accumulator independently of the position of said throttling valve; said throttling valve being moved by said actuator and with respect to said passage in said valve seat member; said aqueous solution consisting of a saturated solution of water and silver iodide having a crystallization temperature greater than for pure water whereby ice crystals in said silver iodide solution first begin to form at a temperature of about 27*F. which subsequently pressurizes the immiscible liquid in said bellows to cause said bellows to axially extend and move said throttling valve toward said valve seat member to restrict refrigerant flow through said passage and thus control the temperature of refrigerant in said evaporator at a value of about 32*F. by the alternating closing and opening of said valve seat passage in proportion to the quantity of ice crystals formed in the solution.
 5. Evaporator temperature control means for an automobile air conditioning system including in series flow relation; a compressor, a condenser, expansion means for reducing refrigerant pressure and an evaporator: a combination refrigerant accumulator and thermally responsive evaporator temperature control assembly placed between the evaporator and the compreSsor inlet; said accumulator including a lower portion for holding liquid refrigerant and an upper portion having an inlet for conducting refrigerant into the interior of the accumulator and an outlet for discharging refrigerant therefrom; a valve seat member supported within the interior of said accumulator between said inlet and said outlet and having a passage therethrough for conducting refrigerant from the interior of the accumulator to said outlet; said valve seat member encircling an elongated thermally responsive valve actuator; said valve actuator including an elongated tubular portion connected to an axially extendable bellows portion; said tubular portion being located in the interior of said accumulator which is directly connected to the evaporator by said inlet; an aqueous solution in said tubular portion which freezes at a temperature of about 32* F; an immiscible liquid with respect to water filling the bellows interior and having a solidification temperature substantially below 32* F; a throttling valve member operably connected to said valve actuator and located downstream from said tubular portion to continuously expose said tubular portion and the aqueous solution therein to refrigerant in said accumulator independently of the position of said throttling valve; said aqueous solution consisting of a saturated solution of water and silver iodide having a crystallization temperature greater than for pure water whereby ice crystals in said aqueous solution first begin to form at a temperature of about 27* F which resultantly produces expansion within the tubular portion to pressurize the immiscible liquid within said bellows portion to cause said bellows to extend axially and move said throttling valve toward said valve seat member to restrict refrigerant flow through said passage and thus control the refrigerant temperature within the evaporator at a value of about 32* F by the alternating closing and opening of said valve seat passage in proportion to the quantity of ice crystals formed in the solution. 